Checking objects including bistable magnetic devices, to be checked for ...

United States Patent m

Hoshino et al.

[54] CHECKING OBJECTS INCLUDING

BISTABLE MAGNETIC DEVICES, TO BE
CHECKED FOR AUTHENTICITY

[75] Inventors: Hidekazu Hoshino; Tatsuya Kurihara,

both of Yokohama, Japan

[73] Assignee: NHK Spring Co., Ltd., Yokohama,
Japan

[21] Appl. No.: 461,247
[22] Filed: Jun. 5,1995

Related U.S. Application Data

[63] Continuation of Ser. No. 90,792, Jul. 12, 1993, abandoned. [30] Foreign Application Priority Data

Jul. 14, 1992 [JP] Japan 4-186845

[51] Int. CI.6 G06K 19/06

[52] U.S. CI 235/493; 902/28

[58] Field of Search 235/493, 487,

235/380, 449; 902/28

[56] References Cited

U.S. PATENT DOCUMENTS

4,081,132 3/1978 Pearce .

4,094,462 6/1978 Moschner 235/449 X

4,114,032 9/1978 Brosow et al 235/493

4,138,057 2/1979 Atalla 235/380

4,218,674 8/1980 Brosow et al 340/149 A

4,450,348 5/1984 Stockburger et al 235/380

4,527,051 7/1985 Stenzel 235/380

4,639,670 1/1987 Normann 324/260

4,660,025 4/1987 Humphrey 340/572

4,820,912 4/1989 Samyn 235/449

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US005583333A [ii] Patent Number: 5,583,333 [45] Date of Patent: Dec. 10,1996

4,859,991 8/1989 Watkins et al 340/572

5,204,526 4/1993 Yamashita et al 235/493

5,434,917 7/1995 Naccache et al 235/380 X

FOREIGN PATENT DOCUMENTS

2471633 6/1981 France .

Primary Examiner—Donald T. Hajec

Assistant Examiner—Jeffrey R. Filipek

Attorney, Agent, or Firm—Frishauf, Holtz, Goodman,

Langer & Chick

[57] ABSTRACT

A number of bistable magnetic devices are dispersed in a scanning region of a checking object. Each bistable magnetic device is formed of a nonmagnetic material which undergoes a drastic flux reversal attributable to the Large Barkhausen effect when subjected in succession to first and second external magnetic fields of opposite directions. A processing apparatus comprises magnetic generators for generating magnetic fields of opposite directions, a transportation mechanism for moving the checking object at constant speed, and a coil for detecting magnetic pulses, which are generated as the bistable magnetic devices are subjected to the flux reversal, as changes of electromagnetic induction voltage. A detection signal for the scanning region detected by the apparatus is converted into a cipher code and then recorded in a code indicator section of the checking object. In checking the authenticity of the object, the detection signal obtained by scanning the scanning region and a code for collation' obtained by decoding the cipher code recorded in the code indicator section are compared, and it is concluded that the checking object is real when the detection signal and the collation code correspond to each other.

12 Claims, 4 Drawing Sheets